There is a conventionally known technique in which a diesel particulate filter (DPF, hereinafter) is provided in an exhaust gas path of a diesel engine as an exhaust gas purification device (post-processing system), and exhaust gas discharged from the diesel engine is purified by DPF (see Patent Documents 1 to 3 for example). There is also a known technique in which an inner case (filter case) is provided in an outer case (casing) in a DPF, and a filter member such as an oxidation catalyst and a soot filter is disposed in the inner case (see Patent Document 4 for example).